The present invention deals with the mixing of pulverized solids and liquids and can be applied, for example to hydraulic binders preparation and specifically to the continuous process preparation of a plaster powder and water mixture.
It is a widespread practice, in order for the mixing of pulverized solids and liquids, to use mixers having teeth or blades and consisting of a cylindrical container having a vertical shaft fitted with one or several sets of revolving radial arms bearing blades or teeth. These blades or teeth scrape the container's walls, mix the products and thus operate a stirring. But such mixers do not provide a satisfactory dispersion of pulverized solid into the liquid; hence there is a lack of homogeneity in the fluidity of the discharged mixture. On the other hand, there are turbine mixers consisting of a container in which a disc, a propeller or a turbine is revolving at very high speed. The solid and the liquid reach the turbine which disperses them instantly. Contrary to teeth mixers, turbine mixers achieve a high shearing rate and an intensive turbulence in all points of the system, so that product dispersion and homogenization are satisfactory. But the study of such a mixer's performance, through the introduction of some colored substance, or generally any tracer substance which can easily be detected, reveals that a variation in the supply is reflected without any change at the outlet after a very brief delay of the order of one second. Thus, in a turbine mixer, the time during which the product remains in the mixer is very short, indeed, so short that irregularities in supply are not suppressed by the mixing operation and still exist unchanged at outlet. When an even fluidity of final product is desired, which is impossible to obtain through evenness of supply, turbine mixers will not be satisfactory.
The present invention obviates the drawbacks of both known systems; it makes it possible to provide a continuous process mixing of pulverized solids and liquids with an even fluidity.
In addition this invention overcomes the problem of premature setting of a fluid evolutive product in the mixer. A fluid evolutive product is a liquid in which a reaction resulting in a physical or chemical transformation takes place producing a solid phase or modifying the characteristics of a solid phase initially carried by the liquid. A plaster powder and water mixture is exemplary of such a product.